Revert most of the change to word break, but introduce a nbsp for browser metrics.

Related to PR 13305: I tried to use zero-width-space to force appropriate
line breaks, but unfortunately under Opera on Linux, this shows as
unsupported character glyphs.

Since I can't reliably use zero-width-space, I'm backtracking to the
prior solution on introducing spans with the mywbr class.  However,
I've added in a &nbsp element to the content of the span, as suggested
elsewhere on the web.  This appears to fix the _gcpointer issue that
Eric sees.